Global Positioning System (GPS) is widely used for, tracking, locating, and navigating purposes. However, “GPS-denied” environments exist in which GPS signals are weak or unavailable due to jamming, weather conditions, or physical obstructions, such as bridges or buildings. Moreover, GPS signals are unavailable for lunar and other space exploration operations. In such GPS-denied environments, other methods and instruments (e.g., astronavigation and Inertial Measurement Units (IMUs), which use a combination of accelerometers and gyroscopes) have been relied on for location and navigation.
However, alternatives to GPS have various disadvantages. For example, gyroscopes drift over time and by definition only provide relative position from a starting point versus an absolute measurement. Moreover, astronavigation provides only crude position resolution and astronavigation.
Some localization solutions that have been proposed in response to the foregoing problems rely on GPS as a complementary locating system. For example, according to one proposed solution, a device that lacks GPS access could communicate with one or more other devices that have GPS access to determine its position relative to the GPS-equipped device(s). However, solutions of this type typically suffer poor localization accuracy and ultimately rely on GPS for operation and are therefore ill-suited for application in every GPS-denied environment.
Another solution provides localization of an individual mobile subscriber using the resources of a cellular network. However, solutions of this type typically suffer poor localization accuracy. As well, localization is not the primary function of a cellular network and therefore typically requires temporary dedication of cellular base transceiver station towers in the neighborhood of the mobile subscriber, thus disrupting other traffic for a time.